jeremy Posted January 26, 2006 Report Share Posted January 26, 2006 What is the PMIII (Taken from Chris A) The DM Powermaster III provides normal service brake boosting function and emergency ABS function. From a completely discharged point, the pump motor will run for 30 to 90 seconds. Brake fluid is stored in the accumulator between 1800 to 2400 psi. Accumulator pressure drops as the booster valve meters pressure to the braking pistons. Fluid is returned to the reservoir when the pedal is released. Every 3 to 5 pedal presses will drop the accumulator pressure below 1800 psi when the pressure switch will ground the motor relay and turn the pump motor on to restore accumulator pressure. Fluid for the accumulator is drawn in from the rear brake portion of the reservoir. Accumulator pressure is also used for ABS braking. The 3 solenoids, 1 each for the front brakes and 1 for both rear brakes, can apply, hold or release brake pressure for each circuit. The accumulator pressure is used for re-apply. Power for the PMIII is provided from several sources. The ABS fuse in the interior fuse box provides an ignition feed to the PMIII relay and module. This is the only ignition control for normal booster operation. The ABS fuse box, located next to the washer reservoir, supplies power for the pump motor, solenoids and relay. The brake pedal should have a firm feel and will not have the same amount of travel a typcially vacuum booster setup would. You can press the pedal to the floor if you try. Braking action should have a linear feel, but again, will not have the same amount of travel a vacuum brake setup would for the same amount of braking action. PMIII Operational Check With ignition off, pump brake pedal 20 to 40 times (discharging accumulator). Turn ignition on and note pump run time. Should be 30 to 60 seconds. Apply brake pedal repeatedly and count number of presses to activate motor. Should be 3 to 5. Allow pump to shut off. Then hold pedal with steady pressure. Pump should not run with steady pedal pressure. Servicable Items and Problems: Pressure Switch: Bad switch can be indicated by a red light on the dash, no pump operation, frequent pump operation, pump not shutting off, pump running too long. Retails for $70 P/N 18013988 Accumulator: Causes frequent pump running (less than every 4 to 5 pedal presses), Pump running under steady pedal pressure, no power assist, Yellow ABS light indicating frequent pump run or long run time. The accumulator is pre-charged to at least 600 psi with nitrogen. The nitrogen can leak out. Retail $140 P/N 18013994 Motor Relay: Erratic Pump running, extended pump running, running while ignition is off, or not running at all Solenoids: Pulling to one side, or ABS trouble code being set. These rarely go bad Rear Pump Housing: The rear pump housing on these units develop cracks over time and high pressure and when the unit is charged (2700 psi) fluid is pressed out thru the small cracks. Retail $270. This item is replaced by Prior Reman with a custom in-house machined piece. For more information, and where this was taken from, and instructions on replacing or converting to Vacuum setup, go here to Chris A's web site http://www.tpsgarage.com/TGP/brakes/powermaster.htm submitted by Prospeeder Link to comment Share on other sites More sharing options...
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